1. Field of the Invention
The present invention relates to a method and apparatus for separating unburned carbon from raw flyash generated from a coal-fired power plant. More particularly, the present invention is directed to a two-stage system which utilizes a centrifugal classifier and a triboelectrostatic separator for separating unburned carbon from raw flyash. The flyash can be used as an additive for concrete, as a stabilizer and filler in civil engineering applications, as an additive to soil, e.g. as a fertilizer, artificial zeolite, and the like.
2. Description of the Related Art
Various types of centrifugal classifier systems and methods for separating unburned carbon from raw flyash are known in the art. Generally, the amount of flyash generated from coal-fired power plants will be increasing in proportion to increases in coal-fired power plant construction. As an example, the amount of raw flyash generated from coal-fired power plants in South Korea in 1990 was about 3 million tons.
Most raw flyash generated from coal-fired power plants has generally been considered a waste product and thus has been used primarily to reclaim land from the sea. However, the reclaimed land has created environmental pollution problems, environmental plant destruction problems, and other related problems.
Recently, recycled flyash produced from raw flyash by centrifugal classifier systems have been used. However, in these systems, unburned carbon is destroyed and forms a contaminant in the ash thus produced. Unfortunately, unburned carbon in the ash absorbs some of the other additives and reduces the concrete strength if the flyash is used as a concrete filler. In this situation, the flyash contains over 7% of unburned carbon. Usually, flyash containing less than 3% of unburned carbon is a valuable flyash.